Electrodeposition of nickel from the sulfamate bath



United States Patent 3,360,445 ELECTRODEPOSITION 0F NICKEL FROM THE SULFAMATE BATH Ramon U. Tobar, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, De]., a

corporation of Delaware No Drawing. Filed Jan. 4, 1965, Ser. No. 423,301 10 Claims. (Cl. 204--3) This invention relates to electrodeposition of nickel and more particularly it is directed to acidic nickel electrodepositing solutions containing nitrate ions and to processes of electrodeposition utilizing such solutions.

Many nickel electrodepositing solutions have been devised in the past. Such solution include batch electroplating and electroforming solutions. Some of these solutions were acidic and some were basic, however, each had some shortcoming either in the quality of the deposit or in the behaviour of the solution.

I have discovered that by including in an acidic nickel electrodepositing solution very small amounts of nitrate ions, I am able to produce consistently excellent deposits of nickel which are pit free and have amazingly low internal stress and improved brightness. Such outstanding deposits are obtainable Whether the deposition is by electroplating or by electroforming.

The nitrate ions can be added to the nickel solution as any water soluble nitrate salt which does not contain cations which detract from the efiectiveness of the electrodeposition process. Such salts as the alkali and alkaline earth metal salts are particularly suitable.

In the practice of this invention nickel is supplied by maintaining in the plating solution a suitable source of nickel such as nickel sulfamate. While good deposits of nickel can be obtained from aqueous solutions containing only nickel sulfamate and a nitrate such as nickel nitrate, it is often desirable to have present in the solution other agents which serve useful purposes.

For instance, in order that an optimum pH range can be conveniently maintained a buffering agent such as boric acid can be included. To further improve brightness of the nickel plate such brightening agents as primary and secondary brighteners conventionally used today in bright nickel plating can be added. Agents such as nickel bromide or nickel chloride can be added to improve anode dissolution by reducing polymerization. Agents such as sodium lauryl sulfate or sodium lauryl sulfoacetate can be added as conventional anti-pitting agents.

While it is commonly accepted that nickel sulfamate baths produce a nickel plate with low tensile stress, it is nevertheless of significant importance that the presence of the nitrate ion enables deposition of nickel with even lower internal stress.

This advantage allows for deposition of bright, pit free nickel while controlling internal stress all the way down to negative, or compressive stress, as desired. It further allows for addition to the bath of other agents which ordinarily are limited by the increased internal stress which they cause. For example, nickel bromide or nickel chloride can be added to increase the anode dissolution thereby making it possible to avoid passivation which will norm-ally occur when using nickel sulfamate alone. Such addition can be made to an electrodepositing solution containing nitrate ions without increasing the internal stress beyond that which is normal for nickel sulfamate solutions.

Representative of specific nitrate salts which are uitable for use in this invention are as follows:

(1) Nickel nitrate;

(2) Ferrous nitrate;

(3) Sodium nitrate;

3,360,445 Patented Dec. 26, 1967 (4) Potassium nitrate;

(5) Calcium nitrate;

(6) Lithium nitrate;

(7) Strontium nitrate;

(8) Rubidium nitrate;

(9) Cesium nitrate;

(10) Zinc nitrate; and

( ll) Cadmium nitrate.

The most suitable nitrate salt for use in this invention is nickel nitrate which provides the necessary nitrate ions as well as additional nickel ions for the electrodepositing solution. 1

The concentrations per liter of solution of the various components in addition to the water can be as follows:

Nickel sulfamate gr./liter to 500 Nitrate ion parts/million 5 to 250 Boric acid (buffering agent) gr./liter 30 to 60 Nickel bromide (corrosion agent) gr./liter 1 to 100 Sodium lauryl sulfate (anti-pitting wetting agent) gr./liter .1 to 1 oBenzoyl sulfimide (brightening agent) gr./liter 1 to 3 As mentioned previously, the buffering agents, corrosion agents, anti-pit agents and brighteners are optional additives and can be excluded entirely, and recitation of the above agents is, of course, merely exemplary of the types of each agent which can be used, when electroplating or electroforming.

In order to achieve a bath which operates with maximum current efliciency it is preferred to use a concentration of nickel sulfamate of from 300 to 450 grams per liter of solution.

Similarly, to achieve maximum stress reduction without impairing efliciency of the nickel deposition, it is preferred to use a concentration of from 10 to 150 parts per million of nitrate ion based on the total solution.

Preferred amounts of the optional additives, if they are used, are exemplified by the following:

Plating processes or electroforming processes utilizing the solution of this invention are most advantageously operated under the following conditions:

pH of 3 to 4.5;

Cathode current density of 20 to 300 amps/ sq. ft;

Temperature of 90 to F.;

Voltage of 2 to 10 volts.

In order that the invention can be better understood, the following illustrative examples are given wherein parts and percentages are by weight unless otherwise noted. In each example the measurements or internal stress of the nickel deposit are made with a spiral contractometer in accordance with the method described by A. Brenner and S. Senderolf in the Proceeding of the American Electroplaters Society, vol. 35, p. 53 (1948).

Exlample 1 A nickel electrodepositing bath composition employed for this and subsequent examples is prepared containing, per liter of solution, approximately 400 grams of nickel sulfamate, 30 grams of boric acid and 0.12 gram of sodium lauryl sulfate. Two liters of this solution are placed in a beaker. The pH of this solution prior to the test is 4.0. The nickel is deposited by the method described in the Proceeding of the American Electroplaters Society, vol. 35, p. 53 (1948). A constant cathode current density of 25 amperes per square foot is applied for 30 minutes at a constant temperature of 120 F. The internal tensile stress measured with the spiral contractometer is then calculated to be 3000 pounds per square inch. The surface of the nickel deposit appears dull with a small amount of pitting.

Example 2 A bath prepared in accordance with Example 1, but containing in addition 0.0118 gram of nickel nitrate hexahydrate [Ni(NO .6H O] per liter or p.p.m. nitrate ion is tested as in Example 1. The internal tensile stress value calculated for the nickel deposited from this solution is 2500 pounds per square inch. The nickel deposit appears brighter than that of Example 1 and no pitting is observed,

Example 3 The standard bath and operating conditions specified in Example 1 are used here, with the exception that 0.0237 gram of nickel nitrate hexahydrate [Ni(NO .6H O] per liter are added to the bath. This provides p.p.m. nitrate ion in the bath. The internal tensile stress value calculated for the nickel deposited from this solution is 2250 pounds per square inch. The process is carried out with increased cathode etiiciency. No pitting is observed in this deposit and its surface is much brighter than the deposit obtained in Example 1.

Example 4 A bath is prepared in accordance with Example 1, but containing in addition 0.1185 gram of nickel nitrate hexahydrate per liter, to provide 50 p.p.m. of nitrate ion. The internal stress is measured as in Example 1 with the Brenner Senderoff spiral contractometer using the same depositing conditions used in Example 1. There is a marked increase in cathode efliciency during deposition as indicated by the increased weight of deposit. The internal tensile stress value of this deposit is calculated to be 1826 pounds per square inch and it is bright and pit free.

Example 5 The same bath and depositing conditions used in Example 1 are used here with the exception that 0.237 gram of nickel nitrate hexahydrate are added per liter to provide 100 p.p.m. of nitrate ion in the bath. The internal stress value of the deposit, measured as in Example 1 is calculated to be 84.8 pounds per square inch, this value is compressive instead of tensile. The deposit is also exceptionally bright and pit free.

Example 6 The same bath composition as described in Example 1 is again employed, but in this case 0.574 gram of nickel nitrate hexahydrate per liter are added to provide 200 p.p.m. of nitrate ion in the bath. The same plating conditions of Example 1 are used here. The calculated internal stress value of the deposit is 374 pounds per square inch. This value is compressive rather than tensile. The nickel deposit is also exceptionally bright and pit free.

Example 7 A nickel electrodepositing bath composition containing per liter of solution, approximately 200 grams of nickel sulfamate, 35 g. of boric acid, 0.12 gram of sodium lauryl sulfate and 0.137 gram of sodium nitrate to provide 100 p.p.m. of nitrate ion is prepared. Two liters of this solution are placed in a beaker. Nickel is then deposited under the same conditions as those of Example 1. A measurement of the internal stress of the nickel deposit is made using the Brenner Senderolf spiral contractometer. The calculated tensile stress value for the nickel deposit is 200 pounds per square inch.

Example 8 The same bath composition as described in Example 7 is employed, but in this case 0.192 gram of cadmium ni- 4 trate tetrahydrate are added to the bath instead of the sodium nitrate. The internal stress of the nickel deposit is determined using the Brenner Senderoff contractometer under the plating conditions described in Example 1. An internal compressive stress of 20 pounds per square inch is calculated and the nickel deposit is bright and pit free.

I claim:

1. An aqueous acidic nickel electrodepositing solution comprising 130 to 500 grams of nickel sulfamate per liter of solution and a sufiicient amount of a nitrate salt to supply 5 to 250 parts per million of nitrate ion in the solution, with the limitation that the nitrate salt must be one which contains no cations which would interfere with a nickel electrodeposition process.

2. An aqueous acidic nickel electrodepositing solution comprising 300 to 450 grams of nickel sulfamate per liter of solution and sufiicient nickel nitrate to supply from 10 to 150 parts per million of nitrate ion in the solution.

3. An aqueous acidic nickel electrodepositing solution comprising per liter of solution 130 to 500 grams of nickel sulfamate, 30 to 60 grams of buffering agent, 1 to 100 grams of anode-corrosion agent, .1 to 1 gram of antipitting agent and from 0.25 to 3 gram of brightening agent and containing sufiicient nickel nitrate to supply from 5 to 250 parts per million of nitrate ion based on the total solution.

4. An equeous acidic nickel electrodepositing solution comprising per liter of solution from 300 to 450 grams of nickel sulfamate, from 30 to 60 grams of boric acid and from 10 to 50 grams per liter of nickel bromide and containing sufficient nickel nitrate to supply from 10 to 150 parts per million of nitrate ion based on the total solution.

5. An electrodepositing process comprising passing a current from an anode to a cathode to be coated through an aqueous acidic nickel solution comprising 130 to 500 grams of nickel sulfamate per liter of solution and a sufficient amount of a nitrate salt to supply 5 to 250 parts per million of nitrate ion in the solution, with the limitation that the nitrate salt must be one which contains no cations which would interfere with a nickel electrodeposition process.

6. The process of claim 5 in which the pH is main tained in the range of 3 to 4.5, the temperature is maintained in the range of to 140 F. and the current density is maintained in the range of 20 to 300 amperes per square foot.

7. An electrodepositing process comprising passing a current from an anode to a cathode to be coated through an aqueous acidic nickel solution comprising per liter of solution 130 to 500 grams of nickel sulfamate, 30 to 60 grams of buffering agent, 1 to grams of anode-corrosion agent, .1 to 1 gram of anti-pitting agent and from 0.25 to 3 grams of brightening agent and containing sufficient nickel nitrate to supply from 5 to 250 parts per million of nitrate ion based on the total solution.

8. An electroforming process comprising passing a current from an anode through an aqueous acidic nickel solution comprising per liter of solution to 500 grams of nickel sulfamate, 30 to 60 grams of buffering agent, 1 to 100 grams of anode-corrosion agent, .1 to 1 gram of antipitting agent and from 0.25 to 3 grams of brightening agent and containing sufiicient nickel nitrate to supply from 5 to 250 parts per million of nitrate ion based on the total solution in which the pH is maintained in the range of 3 to 4.5, the temperature is maintained in the range of 90 to F., and the current density is maintained in the range of 20 to 300 amperes per square foot, to a cathode.

9. An electroplating process comprising passing a current from an anode to a cathode through an aqueous acidic nickel solution comprising per liter of solution 130 to 500 grams of nickel sulfamate, 30 to 60 grams of buffering agent, 1 to 100 grams of anode-corrosion agent, .1 to 1 gram of anti-pitting agent and from 0.25 to 3 grams of brightening agent and containing suflicient nickel nitrate to supply from 5 to 250 parts per million of nitrate ion based on the total solution, in which the pH is maintained in the range of 3 to 4.5, the temperature is maintained in the range of 90 to 140 F., and the current density is maintained in the range of 20 to 125 amperes per square foot.

10. In a bath for electrodepositing nickel and comprising an aqueous acidic solution of nickel sulfamate: the improvement which comprises nickel nitrate dissolved in the bath to supply a concentration of nitrate ions of from 5 to 250 parts per million based on the total solution.

References Cited UNITED STATES PATENTS 2,318,592

6 4/1967 Wells et a1. 204-43 X 6/ 1967 Kendrick et al 204-49 X OTHER REFERENCES 0 can Electrochemical Society, pages 31-35, volume 48,

ROBERT K. MIHALEK, Primary Examiner.

5/1943 Cupery 204 49 15 G. KAPLAN, Assistant Examiner. 

1. AN AQUEOUS ACIDIC NICKEL ELECTRODEPOSITING SOLUTION COMPRISING 130 TO 500 GRAMS OF NICKEL SULFAMATE PER LITER OF SOLUTION AND A SUFFICIENT AMOUNT OF A NITRATE SALT TO SUPPLY 5 TO 250 PARTS PER MILLION OF NITRATE ION IN THE SOLUTION, WITH THE LIMITATION THAT THE NITRATE SALT MUST BE ONE WHICH CONTAINS NO CATIONS WHICH WOULD INTERFERE WITH A NICKEL ELECTRODEPOSITION PROCESS.
 8. AN ELECTROFORMING PROCESS COMPRISING PASSING A CURRENT FROM AN ANODE THROUGH AN AQUEOUS ACIDIC NICKEL SOLUTION COMPRISING PER LITER OF SOLUTION 130 TO 500 GRAMS OF NICKEL SULFAMATE, 30 TO 60 GRAMS OF BUFFERING AGENT, 1 TO 100 GRAMS OF ANODE-CORROSION AGENT, .1 TO 1 GRAM OF ANTIPITTING AGENT AND FROM 0.25 TO 3 GRAMS OF BRIGHTENING AGENT AND CONTAINING SUFFICIENT NICKEL NITRATE TO SUPPLY FROM 5 TO 250 PARTS PER MILLION OF NITRATE ION BASED ON THE TOTAL SOLUTION IN WHICH THE PH IS MAINTAINED IN THE RANGE OF 3 TO 4.5, THE TEMPERATURE IS MAINTAINED IN THE RANGE OF 90 TO 140*F., AND THE CURRENT DENSITY IS MAINTAINED IN THE RANGE OF 20 TO 300 AMPERES PER SQUARE FOOT, TO A CATHODE. 